1366 - Incorrect integer value: '' for column 'customer_id' at row 1

insert into whos_online (customer_id, full_name, session_id, ip_address, time_entry, time_last_click, last_page_url) values ('', 'Guest', '5jttlf2a0sq21tiv1h79802fq7', '216.73.216.72', '1787786090', '1787786090', '/index.php?XTCsid=38f09672db884903e3803adf9d076819&language=en')

[XT SQL Error]